Spool for fuel circuit valve of an aircraft engine

ABSTRACT

A spool for a fuel circuit valve of an aircraft engine, extending along a longitudinal axis and including a narrowed intermediate section extending between two end cylindrical sections, a first end section being separated from the narrowed intermediate section by a shoulder having a surface arranged overall perpendicular to the longitudinal axis, the narrowed intermediate section also including, extending away from the shoulder, at least one cylindrical portion, and the shoulder is provided with a step extending away from the cylindrical surface of the first end section which, when the fuel flows along the first end section towards the narrowed intermediate section and the second end portion, generates a jet of fuel on the cylindrical portion of the narrowed intermediate section, a recirculation of fuel forming in an area in front of the shoulder.

GENERAL TECHNICAL FIELD

The present invention relates to the field of valves for the fuel circuit of an aircraft engine, of the spool/sleeve type. More precisely, the present invention relates to a spool for a valve of an aircraft engine fuel circuit.

PRIOR ART

FIG. 1 illustrates an example of a valve 1 for the fuel circuit of an aircraft engine comprising a sleeve 2 at the interior of which is provided a spool 3 extending along a longitudinal axis 4.

The sleeve 2 comprises a first chamber 5 provided with a fuel inlet 6 and a second chamber 7 provided with a fuel outlet 8, the first and the second chambers 5, 7 being connected to one another via a duct 9. The sleeve 2 also comprises two control chambers (not shown) allowing the induction of a displacement of the spool 3 along the longitudinal axis 4 depending on the pressure differential between these two chambers.

The spool 3 comprises a first cylindrical portion 10 extending into the first chamber 5, a second cylindrical portion 11 extending into the second chamber 7 and a third portion 12 connecting the first and second portions 10, 11 and at which the cross section area of the spool 3 is narrowed. The spool 3 is displaced along the longitudinal axis 4 under the influence of a pressure differential between the two control chambers, between a closed position in which the first portion 10 of the spool 3 blocks the duct 9 so as to prevent the flow of fuel from the fuel inlet 6 to the fuel outlet 8, and an open position in which the first portion 10 of the spool 3 frees the duct 9 so as to allow the flow of fuel from the fuel inlet 6 to the fuel outlet 8.

Now with a valve 1 of this type, in the open position, the fuel flow does not have the same movement quantity between the fuel inlet 6 and the fuel outlet 8. In fact, the difference in the cross section area between the first portion 10 and the third portion 12 generates, in the open position, a fuel jet which applies an additional load on the spool 3. This additional load, also called a “jet force” is particularly problematic because it includes an axial component which perturbs the control of the spool 3 by differential pressure. It will in fact be understood that any additional axial load applied to the spool 3 causes an error in the positioning of the spool 3 and consequently generates inaccuracies as to the flow rate of fuel at the outlet of the second chamber 7. The jet force is therefore harmful to the correct operation of the fuel circuit.

To avoid such inaccuracies, it is known for example from document WO 80/00870 to provide in the spool one or more grooves extending longitudinally, having a rounded longitudinal profile and the radius of curvature whereof is determined so that the fuel jet enters and leaves the groove while forming the same angle of approximately 69° with the longitudinal axis. This allows a reduction in the effects of the jet force on the spool. This reduction, however, is not sufficient to ensure the required accuracy for proper operation of the fuel circuit.

There is therefore a need to further limit the effects of jet forces on the spools of the aircraft engine fuel circuit.

PRESENTATION OF THE INVENTION

The present invention responds to this problem by proposing a spool for a valve of an aircraft engine fuel circuit which comprises a shoulder provided with a step ensuring an inflow of the fuel jet generated by said shoulder on a cylindrical section of the spool and a recirculation of the fuel in front of the shoulder. In this manner, the generation of an axial load which would tend to displace the spool axially is avoided.

More precisely, the present invention has as its object a spool for a valve of an aircraft engine fuel circuit extending along a longitudinal axis, and comprising a narrowed intermediate portion extending between two cylindrical end portions, a first end portion being separated from the narrowed intermediate portion by a shoulder having a surface arranged perpendicular to the longitudinal axis overall, the narrowed intermediate portion itself including, as an extension of the shoulder, at least one cylindrical section.

The shoulder is provided with a step which is a protuberance protruding with respect to said shoulder, as an extension of the cylindrical surface of the first end portion which, when fuel flows along the first end portion in the direction of the narrowed intermediate portion and of the second end portion, ensures the generation of a fuel jet on the cylindrical section of the narrowed intermediate portion, a recirculation of fuel forming in a zone in front of said shoulder.

According to one embodiment, the step in particular extends substantially perpendicularly from the surface of the shoulder.

Preferably, the shoulder comprises at least one groove which extends radially from the cylindrical surface of the first end portion, in the direction of the longitudinal axis, until the cylindrical section of the narrowed intermediate portion. This groove forms a fuel recirculation zone which ensures, when fuel flows along the first end portion in the direction of the narrowed intermediate portion and of the second end portion, that the fuel jet generated arrives on said cylindrical section.

The step extends from said groove, so as to accelerate the recirculation of the fuel in the recirculation zone.

Preferably, the groove extends longitudinally from the shoulder on the cylindrical section of the narrowed intermediate portion and the groove has, at said cylindrical section, a flat bottom overall, the fuel jet generated by the groove reaching said cylindrical section at the bottom of said groove.

In one embodiment, this step extends substantially perpendicularly from the surface of the shoulder.

The invention also has as its object a valve for an aircraft engine fuel circuit, comprising a sleeve, in the interior of which is provided a spool as previously described, said sleeve comprising two control chamber between which the spool extends and an intermediate chamber provided with a fuel inlet and a fuel outlet in which the first and the second end portions and the narrowed intermediate portion of the spool extend, the spool being configured to be displaced relative to the sleeve under the influence of a pressure difference between the two control chambers, between a closed position in which the spool blocks the fuel inlet, and an open position in which the spool frees the fuel inlet.

The invention also has as its object an aircraft turbomachine fuel circuit comprising a valve as previously described.

The invention also has as its object an assembly including an aircraft turbomachine and a circuit of this type, as well as an aircraft comprising a turbomachine connected to a fuel circuit of this type.

PRESENTATION OF THE FIGURES

Other features, aims and advantages of the present invention will appear upon reading the detailed description that follows, and with reference to the appended drawings given by way of non-limiting examples and in which:

FIG. 1 shows a schematic view, in longitudinal portion, of a valve for an aircraft engine fuel circuit of the spool/sleeve type according to the prior art,

FIG. 2 shows a partial schematic view, in longitudinal portion, of a valve for an aircraft engine fuel circuit of the spool/sleeve type according to one embodiment of the invention,

FIG. 2a shows a detail view of the valve illustrated in FIG. 2,

FIG. 3 shows a perspective view of the spool of the valve illustrated in FIG. 2, and

FIG. 4 shows a front view of the spool illustrated in FIG. 3.

DETAILED DESCRIPTION

FIG. 2 illustrates an example of a valve 20 for an aircraft engine fuel circuit. The valve 20 comprises in particular a sleeve 21, in the interior of which is provided a spool 22 extending along a longitudinal axis 23.

The sleeve 21 comprises two control chambers 231, 232 allowing the induction of a displacement of the spool 22 along the longitudinal axis 23 depending on a pressure differential between these two chambers. The sleeve 21 also comprises an intermediate chamber formed from a first chamber 24 provided with a fuel inlet 25 and a second chamber 26 provided with a fuel outlet 27, the first and the second chambers 24, 26 being connected to one another via a duct 28.

The spool 22 extends between the two control chambers 231, 232 in the intermediate chamber.

The spool 22 comprises a narrowed intermediate portion 32 extending between two cylindrical end portions 29, 31, a first end portion 29 being separated from the narrowed intermediate portion 32 by a shoulder 36 having a surface 37 arranged perpendicularly overall with respect to the longitudinal axis 23. The narrowed intermediate portion 32 includes, as an extension of the shoulder 36, at least one cylindrical section 34. The narrowed intermediate portion 32 can also include a frustoconical portion 35 connecting the cylindrical section 34 to the second end portion 31 of the spool 22.

The spool 22 is displaced along the longitudinal axis 23, under the influence of the pressure differential between the two control chambers 231, 232, between a closed position in which the first end portion 29 of the spool 22 blocks the duct 28 so as to prevent the flow of fuel from the fuel inlet 25 to the fuel outlet 27, and an open position in which the first end portion 29 of the spool 22 frees the duct 28 so as to allow the flow of fuel from the fuel inlet 25 to the fuel outlet 27. In the open position, the sudden change of portion between the first end portion 29 and the narrowed intermediate portion 32 causes the generation of a jet of fuel on the narrowed intermediate portion 32.

The shoulder 36 is provided with a step 42 extending away from the cylindrical surface 30 of the first end portion 29. This step 42 is a protuberance protruding with respect to the shoulder 36. It provides a recirculation of the fuel in front of the shoulder (recirculation zone 40) and thus the generation of a fuel jet on the cylindrical section 34 of the narrowed intermediate portion 32, when the fuel flows along the first end portion 29 in the direction of the narrowed intermediate portion 32 and of the second end portion 31. The step 42 allows a reduction in the effect of fuel pressure on the spool 22. The step 42 is shown in more detail in FIG. 2 a.

The step 42 extends substantially parallel to the longitudinal axis 23 from the shoulder 36. In other words, the step 42 is arranged substantially perpendicular to the shoulder 36 and to the radial surface 37 defining it. What is meant by “substantially parallel” or “substantially perpendicular” is parallel or perpendicular within the limits of error, i.e. within 10°.

The shoulder 36 can also comprise at least one groove 38 which extends radially from the cylindrical surface 30 of the first end portion 29, in the direction of the longitudinal axis 23, until the cylindrical section 34. The groove 38 provides for recirculation of the fuel in front of the shoulder (recirculation zone 40) and thus the generation of a fuel jet on the cylindrical section 34 of the narrowed intermediate portion 32, when fuel flows along the first end portion 29 in the direction of the narrowed intermediate portion 32 and of the second end portion 31. The groove 38 allows a reduction in the effect of the fuel pressure on the spool 22.

The step 42 extends from said groove 38, so as to accelerate the recirculation of fuel in the recirculation zone 40. In this case, the step 42 forms a protuberance arranged preferably over the entire width of the groove 38.

The step 42 is shown in more detail in FIG. 2 a.

The groove 38 comprises a surface 39 disposed perpendicularly overall to the longitudinal axis 23, set back from the surface 37 of the shoulder 36 with respect to the second end portions 31.

The fuel recirculation zone 40 thus formed is positioned under the fuel jet, i.e. between the fuel jet and the spool 22. The fuel vortices generated at the fuel recirculation zone 40 allow the angle with which the fuel jet arrives on the narrowed intermediate portion 32 to be limited, and thus ensures that the fuel jet arrives on the cylindrical section 34 and not on the frustoconical portion 35 of the narrowed intermediate portion 32. Moreover, the recirculation of fuel allows a reduction in the effect of fuel pressure on the spool 22.

It will be understood that due to the cylindrical shape of the cylindrical section 34, the fuel jet applies no axial load on the cylindrical section 34 tending to displace the spool 22 longitudinally, and that in this case the only axial component applied to the spool 22 corresponds to frictional forces of the fuel. These frictional forces being negligible, the jet force is thus considerably limited. On the other hand, without the step 42 and without the recirculation zone 40, the fuel jet would threaten to reach the frustoconical portion 35 of the narrowed intermediate portion 33, generating as a result an axial force perturbing the positioning of the spool 22. Moreover, unlike the prior art which tended to compensate the deviation in movement quantity between the inlet and the outlet of the valve, the present invention tends not to generate any movement quantity deviation between the inlet and the outlet 25, 27 of the valve 20.

By accelerating the recirculation of fuel in the recirculation zone 40, the load generated by the fuel pressure in the recirculation zone 40 on the surface 39 of the groove 38 is limited. It is thus possible to reduce even more the axial load generated on the spool 22 and in particular to compensate the frictional forces generated by the flow of fuel on the spool 22.

Preferably, the groove 38 is extended longitudinally from the shoulder 36 one the cylindrical section 34 of the narrowed intermediate portion 32. The groove 38 has the effect of avoiding turbulence in the fuel flow, when the valve 20 is in the open position, and thus to limit hammer phenomena in the spool.

The groove 38 has, at the cylindrical section 34, a flat bottom 41 overall, the fuel jet generated by the groove 38 reaching said cylindrical section of the bottom 41 of said groove 38.

The spool 22 comprises for example two grooves 38 provided diametrically with respect to one another.

The groove 38 also has a fillet 381 between the surface 39 of the groove 38 and the bottom 41 of said groove 38, configured to maintain the recirculation of the fuel in the recirculation zone 40. To this end, the fillet 381 is dimensioned so as to maintain the recirculation of the fuel in the recirculation zone 40. The fillet 381 facilitates setting the fuel in motion at the recirculation zone 40 and therefore the recirculation of said fuel in said recirculation zone 40.

The valve 20 and more specifically the spool 22 have the advantage of reducing the jet forces which are applied to the spool 22 by forming a fuel recirculation zone 40 by means of the step 42 and by ensuring that the fuel jet generated by the shoulder 36 arrives on the overall cylindrical section 34 of the spool 22. The valve 20 therefore allows avoiding having the flow of fuel apply an axial load on the spool 22. 

The invention claimed is:
 1. A spool for a valve of an aircraft engine fuel circuit extending along a longitudinal axis, the spool comprising: a narrowed intermediate portion extending between first and second cylindrical end portions, the first cylindrical end portion being separated from the narrowed intermediate portion by a shoulder having a surface arranged perpendicular to the longitudinal axis overall, the narrowed intermediate portion including, as an extension of the shoulder, a cylindrical section, wherein the shoulder is provided with a step which is a protuberance protruding with respect to said shoulder as an extension of a cylindrical surface of the first cylindrical end portion and which, when fuel flows along the first cylindrical end portion in a direction of the narrowed intermediate portion and of the second cylindrical end portion, ensures generation of a fuel jet on the cylindrical section of the narrowed intermediate portion, a recirculation of fuel forming in a recirculation zone adjoining said shoulder, and wherein the shoulder comprises a groove which extends radially from the cylindrical surface of the first cylindrical end portion, in a direction of the longitudinal axis, and from which extends the step, so as to accelerate the recirculation of the fuel in the recirculation zone.
 2. The spool according to claim 1, wherein the step extends substantially perpendicularly from the surface of the shoulder.
 3. The spool according to claim 1, wherein the groove extends longitudinally from the shoulder on the cylindrical section of the narrowed intermediate portion and wherein the groove has, at said cylindrical section, a flat bottom overall, the fuel jet generated by the groove reaching said cylindrical section at the bottom of said groove.
 4. A valve for an aircraft engine fuel circuit, comprising: a sleeve, in an interior of which is provided a spool according to claim 1, said sleeve comprising two control chambers between which the spool extends and an intermediate chamber provided with a fuel inlet and a fuel outlet wherein the first and the second cylindrical end portions and the narrowed intermediate portion of the spool extend, the spool being configured to be displaced relative to the sleeve under an influence of a pressure difference between the two control chambers, between a closed position wherein the spool blocks the fuel inlet, and an open position wherein the spool frees the fuel inlet.
 5. An aircraft turbomachine fuel circuit comprising a valve according to claim
 4. 6. An assembly comprising an aircraft turbomachine and a fuel circuit according to claim
 5. 7. An aircraft comprising a turbomachine connected to a fuel circuit according to claim
 5. 8. The spool according to claim 1, wherein the narrowed intermediate portion includes a frustoconical portion connecting the cylindrical section to the second cylindrical end portion.
 9. The spool according to claim 3, wherein the groove incudes a fillet between the flat bottom and a surface of the groove disposed perpendicular to the longitudinal axis and set back from the shoulder with respect to the second cylindrical end portion. 